1. Field of the Invention
This invention relates to an optical pointing device, more particularly to an optical pointing device that employs laser technology.
2. Description of the Related Art
Speckles arise when a coherent light 2, such as a laser beam, is scattered from a surface 1′, as illustrated in FIG. 1. Accordingly, when the light 2 is scattered from different parts of the surface 1′, different speckle patterns 21 are produced.
Referring to FIG. 2, a conventional optical mouse 3 is shown to include a casing 31, a laser light source 321, a laser light sensor 322, and a processing unit 33. The casing 31 includes a bottom part 311 that is formed with an opening 312. The light source 321 is mounted in the casing 31, and emits light that is directed through the opening 312 in the bottom part 311 of the casing 31, that is incident on a working surface 1, and that is subsequently reflected by the working surface 1 back into the casing 31 through the opening 312. The light sensor 322 is mounted in the casing 31, and detects the light reflected by the working surface 1. The processing unit 33 is mounted in the casing 31, is coupled to the light sensor 322, and is operable so as to determine displacement of the casing 31 relative to the working surface 1 based on the reflected light detected by the light sensor 322 when the casing 31 is moved along the working surface 1. The processing unit 33 generates a control signal that corresponds to the relative displacement of the casing 31 determined thereby and that can be used to control a cursor (not shown) on a computer screen (not shown).
The aforementioned conventional optical mouse 3 is disadvantageous in that when the casing 31 is moved a distance (d) away from the working surface 1, as illustrated in FIG. 3, since the intensity of the light reflected by the working surface 1 does not fade easily in contrast to light produced by non-coherent light sources, the light sensor 322 is still able to detect speckle patterns 323 corresponding to the reflected light, thereby resulting in unintentional movements of the cursor.